3 H-TREES IDEALLY HAVE ZERO SKEW AND RELATIVELY LOW METAL RESOURCE REQUIREMENTS, BUT IN PRACTICE SEE SIGNIFICANT SKEWS, EVEN LOCALLY, BECAUSE OF MISMATCHES IN LOADING, PROCESSING, AND ENVIRONMENT AMONG THE BRANCHES

12.3 H-trees ideally have zero skew and relatively low metal resource requirements, but

in practice see significant skews, even locally, because of mismatches in loading,

processing, and environment among the branches. Clock grids have low local

skew because they short together nearby points, but can have large global skew and

require lots of metal and associated capacitance. The hybrid tree/grid achieves low

local skew because of the shorting without using as much metal as a full clock grid.